JavaServer Pages (JSP) Roseindia

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JavaServer Pages along with HTML, XML templates, and Java code is used by developers to develop dynamic web content.

JavaServer Pages (JSP) is used to develop dynamic web content on the server
using HTML, XML templates, and Java code. JSP is extensively used because it is
portable, secure, fast, and independent of server platforms. JSPs are HTML pages
that get compiled into Java servlets the first time they are invoked.

Web server after recognizing a .jsp file extension pass the request to the
JSP engine. The request is then translated into a Java class, which is then
compiled into a servlet.

Translation and compilation occurs only when the JSP file is requested for
the first time. Thereafter, the request directly goes to the servlet byte code.

init() method is called to initialize the Servlet when it is first loaded
into the virtual machine.

Each request is sent to service() method, which creates a new thread to
generate a response.

Request received is converted into a Java object of type HttpServletRequest,
which is passed to the Servlet along with an HttpServletResponse object that is
used to send the response back to the browser.

Components of JSP

JSP tags are almost similar to XML tags.

JSP Tags can be of two types: One will have a start tag with
optional attributes, body and a matching end tag while the other
will have an empty tag with attributes.

Attribute values in the tag always appear in "" quotes.

Any whitespace in the JSP is read and preserved during
translation into a servlet.

\ is used as an escape character in a tag

A JSP page can be categorized into:

Part that is processed on the server

Template data

Part of the JSP which is processed on the server, can be categorized
into:

JSP Directives

JSP directives are messages by JSP to JSP container that set global values.
They do not produce any output to the client. JSP directives affect a particular
JSP file.

JSP Directives are characterized by the @ character within the tag

There are 3 JSP Directives:

page

include

taglib

Scripting elements

Scripting elements are used to declare variables and methods, evaluate an
expression and include scripting code within the JSP.

There are three types of Scripting elements:

Declaration - is used to define class-wide variables and
methods. Declarations are initialized when the JSP page is
initialized. Methods and variables defined under Declaration are
available throughout JSP page.

Scriptlets - consists of one or more valid Java statements
enclosed between <% and %>. They are executed at
request-processing time. What the Scriptlet actually does
depends on the code. They can modify objects inside them as a
result of method invocations or show output.

Expressions - is a shorthand notation for a scriptlet
enclosed within <%= and %> that outputs a value. When the
expression is evaluated, the result is converted to a string and
displayed. If any part of expression is an object, the
conversion is done using the toString() method of the object.

Standard actions

Standard actions are tags that alter the runtime behavior of the
JSP and enhance the response sent back to the client.